A better understanding of the biochemical basis of taste sensation is the broad aim of this project. The mechanisms of recognition of stimuli at the level of the plasma membrane and the specificity of taste receptor sites in the membrane are being studied. Binding interactions of taste-stimulus compounds are measured directly in vitro using 3H-labeled taste ligands. Plasma membranes are isolated from the taste tissue of the channel catfish Ictalurus punctatus. The membranes are isolated by ultracentrifugation on sucrose density gradients. They are then characterized using marker enzymes and electron microscopy. The binding characteristics have been measured of several amino acids known to be taste stimuli to this species. Definition of the site specificities of taste receptor cell membranes is leading to a better understanding of the determinants of specificity at the peripheral level for the sense of taste.